Administration: Update dashboard welcome panel for 6.3.

Update the background image and styles for the Welcome Panel. This iteration does not use different colors on the admin color schemes, so the CSS for that has been removed. This also adds back in a working "Edit styles" link, which was removed in 6.2 because the link was broken.

Props richtabor, markoserb.
Fixes #58545.


Built from https://develop.svn.wordpress.org/trunk@56291


git-svn-id: http://core.svn.wordpress.org/trunk@55803 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/dashboard.php

@@ -2098,6 +2098,7 @@ function wp_welcome_panel() {
 			<?php if ( $is_block_theme ) : ?>
 				<h3><?php _e( 'Switch up your site&#8217;s look & feel with Styles' ); ?></h3>
 				<p><?php _e( 'Tweak your site, or give it a whole new look! Get creative &#8212; how about a new color palette or font?' ); ?></p>
+				<a href="<?php echo esc_url( admin_url( '/site-editor.php?path=%2Fwp_global_styles' ) ); ?>"><?php _e( 'Edit styles' ); ?></a>
 			<?php else : ?>
 				<h3><?php _e( 'Discover a new way to build your site.' ); ?></h3>
 				<p><?php _e( 'There is a new kind of WordPress theme, called a block theme, that lets you build the site you&#8217;ve always wanted &#8212; with blocks and styles.' ); ?></p>